Electronic power tube tester



April 27, 1948- A. s. ORAV ETZ 2,440,287.

ELECTRONIC POWER TUBE TESTER Filed July 25, 1945 Q 3 Sheets-Sheet 1 STARTING VOLTAGE.

VqL-rs AcRoss Tuas PLATE Cumrsur W: FILAM t n T TRANSFORMER.

INVENTOR. HLBE/ZT 5. OIEHVETZ.

BY To D.C. W SOURCE.

ATTORNEY April 27, 1948.

A. S. ORAVETZ ELECTRONIC POWER TUBE TESTER Filed July 25, 1945 3 Sheets-Sheet 2 35.3: 5 3mm u .21, win! :3

INVENTOR HLBEET 5 OEAVETZ.

ATTORNEY P 7, 1948. A. s. ORAVETZ 2,440,287

ELECTRONIC POWER TUBE TESTER Filed July 25, 1945 3 Sheets-Sheet 3 var scene;

MOGUL. SOCKET INDUSTEIRL Soc x5 1' VaL'IQil wa mi 1 fifb. 5' 1 BY ATTORNEY Patented Apr. 2?, 1948 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates to an electronic-tube tester for measuring the operating characteristics of rectifier tubes with particular application to determining the end of the useful life of the tubes. This tube tester is designed in such a manner as to provide a single portable test unit with which a plurality of tests may be made, and which may be easily transported from one station to another and operated by comparatively unskilled personnel. One instance in which a test unit of this type is of great value is upon repair ships for testing tubes used, for example, in navigational equipment.

An object of this invention is to provide a test unit for measuring the operating characteristics of rectifier tubes. 7

Another object is to provide a test unit for measuring the operating characteristics of gasfilled rectifier tubes.

A further object is to provide a. method and apparatus for measuring average arc-drop for full-wave gas-filled rectifier tubes.

These characteristics are more fully defined as follows:

Starting voltage: The value or the positive anode potential relative to the cathode that is necessary to initiate the conduction current.

Average arcedrop voltage: The average potential between the anode and the cathode during the period in which the tube is passing current.

Critical grid current: The value of the grid current at the start of the conduction current.

Maximum forward voltage (R. M. S.) The highest value of the anode voltage relative to the cathode at which the grid retains control.

Still another object is to provide a single port'- able test unit of the type described which may be operated by relatively unskilled personnel.

Further objects and advantages of this invention, as well as its construction, arrangement and operation, will be apparent from the following description and claims in connection with the accompanying drawings, in which,

Fig. 1 is a graphical illustration of the wave shape of voltage and current in agrid-controlled power rectifier tube,

Fig. 2 is a front perspective view, slightly distorted for the purpose of clarity, of the electronic tube tester of this invention,

. Fig. 3 is a diagrammatic illustration of the electrical circuits of the apparatus of Fig. 2, and

Fig. 4 is a partial wiring diagram of the apparatus of Fig. 2.

The tube tester of this invention is designed to test tubes meeting both Navy and commercial specifications. Among the tubes that may be tested are commercial tubes EL-ClA, EL-C5A,'

EL-CGA, EL-SBHD, and EL-BCF and their Navy equivalents.

For the purpose of illustration only, in the following description and drawings of the tube values assigned the equipment (transformers, rheostats, resistances, indicating instruments, etc.) are those suitable for usein testing rectifier tubes of 0.5, 2.5 and 5.0 ampere ratings. These values may optionally be changed by one skilled in the art for testing tubes'of other types and ratings without departing from the principles of this invention as disclosed herein.

Figure 2 shows a box-like structure or receptacle, generally designated as H, having a metal frame [2, a front or control panel 13, a tube bank It, a top control panel l5, and a top panel It. The top panel l6, side and back panels (not shown) are removably attached to the frame [2 and are preferably perforated as at l! to promote cooling of the interior by convection currents.

Power is supplied the tester through insulated cable l8 entering the rear of the tester II and passin to toggle action on-oif switch S--l in the front control panel l3. The supply cable I8 is provided with a third conductor l9 which is connected to the inside of the metal frame l2 and extends through the plug 20 of the supply cable l8. The third conductor 19 is provided with a lug 2| for connection to a ground.

The front control panel [3 is further provided with a green pilot light 22 for indicating completion of the plate circuit; a red pilot light 23 for indicating completion of the filament circuit; a Plate current control knob 24 for controlling plate current in one ampere range which may be from 2.5 to 5.0 amperes; a Plate current control knob 25 for controlling plate current in another ampere range which may be in the order of 0.5 ampere; a D. C. ammeter 26 for indicating rectified current; an Arc drop meter 21 for indicating arc drop volts when using a plate current in the higher or 2.5 and 5.0 ampere range; an Arc drop meter 28 for indicating arc drop volts when using a plate current in the lower or 0.5 ampere range; a volt meter 29 for indicating filament and plate voltage; a push-button switch 8-6 for providing additional'grid resistance when testing tubes in the higher or 5.0 ampere range; a push-button switch S5 for providing additional grid resistance when testing tubes in the lower or 0.5 ampere range; 2. Grid voltage control knob 30 provided with a dial 3|; a Filament voltage control knob 32; a Plate voltage control knob 33; a push-button switch S-8 for providing one voltage range on voltmeter 29; a push-button switch S--9 for providing another voltage range on voltmeter 29; and a pushbutton switch S-l for selectively placing the voltmeter 29 across the plate, or filament circuits. All controls are provided with appropriate name plates 34.

The tube bank I4 is provided with a Mogul open. -Thiscondition occurswhenthe tube under 33 for receiving tubes of for example, 2.5 and 5.0 ampere ratings, and a UK socket 3! for receiving tubes of for example 0.5 ampere rating. The bases of these sockets are provided with switch operating means to be describedbelow.

Upon the top control panel 15 .is a .Plate transfer switch Sl2 for transferring from one plate to the other in testing full wave rectifier tubes; a grid terminal 33 and lead 39 having a clip 45 for connecting the grid terminal of a tube in the Mogul socket 35 or;industrial socket 36 to the grid circuit of the tube tester; a .plate terminal ii and lead 42 having a clip 43 for connecting the plate terminal of a tube in the Mogul socket or industrial socket 36 to. the plate circuit of the tube tester;.-a.plate terminal M and lead 45 having a clip..45 .for connecting the plate terminal of'a tube in the UK socket 3 1 to the plate circuitof the tube tester; ianda selector switch 8-49 for providing proper load resistance in the plate circuit.

In Fig. 3, for the purpose of illustration only, a full-wave rectifier tubel having two .plates ila and lib is shown opposite. the industrial socket 36, a grid-controlled. rectifiertube 48 is shown opposite the Mogul socket 35, and another grid-controlled rectifier-tube a9 is shown .opposite the UK socket 3,1, with all circuits complete to each tube. Actually only one tube would. -be placed in the tester at a time. Thus oneof the tubes shown wouldbe placed .in-one of the three sockets depending upon its type of base and its ampere rating. TheUX socket isprovided with .a grid connection as showniin. Fig- 4 and is therefore used for tubes having. grid. terminals at their base. Optionally, any number-of sockets with circuits complete to-each may be. provided depending upon the number of tubes of .diiferent types to be tested.

Power is supplied to .the tester from analterhating-current supply which may be 1.15 v., 60 .cycle, through the plug as, conductors 59 .and switch S-i and fuses. 52. The frame I2 is grounded as at 53.

The plate voltage is suppliedbya plate transformer 55, the primary 5'! of which isconnected to the power source through conductors 58 and 59, magnetic relay 583, and conductors Stand 62. The green pilot lamp. is connectedacross the conductors 6i and 62 and lights when the mag netic relay to energizes the plate transformer 56.

Magnetic relay {ii} is energized bytime delay mechanism 63. This device; fisprovides a. time ,delayafter the insertion of a tube into a socket .toallow the filament to come to .normaloperating temperature before the plate voltage is applied. This delay unit 63 may consist of switch .inotor M is disconnected and the line voltage is applied to plate transformer. 5%. A magnetically .operated brake or other electrically responsive means (not shown) holdsthe contact arm and switch 6 in the closed position so that when the circuit to the time delay relay 63 is broken the contact arm and switch 64 return to-their original positions causing the plate circuit to test is removed. from 'itswsocket; or when the power supply is interrupted.

The base of each socket 35, 36 and 31 is provided with a pin 68, which operates when a tube ;is properly placed in the socket to close a switch below the socket thereby completing the circuit to the timedelay mechanism 63. At the bottom iofetheU-Xsocket 3! is a double-pole double-throw relay 63. When, for example; a tube: is placed in the industrial socket 36, the pin 68 is depressed closing the witch's-"2 and completing the circuit from the supply source through conductors 69, I0 switch.S -'2, conductors and i2to the synchronous motor M. After threaminutes thecircuit to the plate transformer 56 closes. p

The plate voltage is controlled by an adjustable auto-transformer 13 connected across the :secondary coil of the transformer-55hr; means of whichv the plate voltage may. bevaried from zero to ,line voltage, whichfor. .examplemayibe v. An additional transformer 14 is also provided for steppingrup the plate voltage to for example 450 volts. "This transformer I4 is selectively introduced into the plate circuit bymeans-of switch S-Il and is so connectedi'that thevoltage supplied may be varied from 0450 also'by means of auto-transformer 13.

.The .Switch Sl l, indicated. upon the control panel l3..as iPeak forward voltage, comprises a double-throw triple-pole leaf switch. Normally the following, contacts are closed; contacts.2 and 3.providing plate voltage in the 0-110 volt range; contacts-5 and 6: connecting the voltmeter. 29 and resistances or voltage multip1iers,R l3 andB-ld across the plate circuit; and contacts 8 and 9 connectingthe. potential coils. of arc-drop. meters Z'Land 28aacnossljtheplate circuit. When the grid-control knob 30 is. turned to the extreme left so that the pointtlla pointsto the Peak forward voltage.position the switch S.II operates. as follows; contacts 2 and? are opened and contacts. i and zaneclosed thereby-shifting the plate voltage from the 0410 volt to thou-450 volt range and increasing the load resistanceby introducing resistance R.-5 into the plate circuit; contacts 5.and.6.are opened and. contacts 4' and 5 are closed thereby introducing voltage multiplier RI5 into series circuit with the voltmeter 29; and contactst and dare opened-and contacts I and 8 are closed .thereby opening .thecircuit to the potential coils of thearc-drop.meters.21.and.28 so as to. prevent damage to vthesemeters .due to high voltages. Theswit'ch- .S-ll is held ,in its normal position ,by'spring tensionior other yieldable retaining means. During the peak-forward voltage test thegrid-controlknob 3,0. is held at the peakaforwardvoltage position and returns to normal position automatically when released.

One. portion of the plate circuit may be traced from the. auto-transformer. "through conductors 75 and T6 to center taps in the filament transformer windings .(described below).

With the switch S-Il in normal position so windings.

R9 and R--I 0, through conductor 80, and when,

a tube is in either the industrial socket 36 or mogul socket 35, through an instrument shunt 8 I which may be of 6.0 ampere rating, conductor 8Ia, the current coil of arc drop meter 21, and conductor 82 to the plate tenminal 4| located on the top control panel I3 (see Fig. 4) Fig. 3 shows the circuit complete from conductor 82 to'the plate of tube 48 through conductor 83. Actually this conductor corresponds to the plate terminal lead 42 shown on the top control panel I3 (Fig. 2).

Fig. 3 also shows the circuit complete from conductor 82 to one of the plates oi the full-wave rectifier tube 41 opposite the industrial socket 36, through conductor 84 and switch S-I2. As shown in Fig. 4, the industrial socket is pro- Vided with plate connections 85 to one plate of the tube under test and 86- to the other plate of the said tube. These connections lead to the switch SI 2, also located on the top control panel I3 (Fig. 2), by means of which either plate of the tube under test may be selectively placed in the plate circuit. Conductor 84 (Figs. 3 and 4) connects the switch S'I2 to the plate terminal When a tube is in the UX'socket 31,-the plate circuit may be traced beginning at conductor 80 through an'instrument shunt 81 of lower ampere rating, for example 0.6 ampere, a fixed resistor R-II, a variable resistance RI2, the current coil of arc drop meter 28, and conductor 88 to the plate terminal 44 above UX socket 31 (Fig. 4) Fig. 3 shows the conductor 88 going directly to the plate of the tube 49 opposite the UX socket. Actually this connection is made from plate terminal 44 through lead 45 on the top panel of the tester (seeFig.2)". t

The plate ammeter 26 has two current ranges,

for'example 0-6 and 0-0.6.amperes. The proper range is automatically "selected by the insertion of a tube into itsprope'r socket. This ammeter 26 is connected through'switch 'S-4 located at the bottom of the UK. socket 44 to either shunt BI or shunt 81. Withno tube in the UX socket 31, the switch S-.-4' connects the ammeter 28 across the terminals of the shunt BI through conductors 89, 90 contacts 3"an'd 4 of theswitch.S-4 and conductors 9 I. With a tube in the UX socket the ammeter 26 is connected across the shunt 81 through conductors 89, 90, contacts4 and '5 of the switch S-4 and conductor 92.

The meters 21 and 28, which are actually wattmeters calibrated to indicate arc dropvolts directly, as will be described below, are so connected that the current coil of the arc dropmeter 28 is in the plate circuit leading to the plate terminal 44 above the UX socket 31, and the current coil of the arc drop meter 21 is in the plate circuit leading to the plate terminal 4i at the mogul andindustrial sockets (see Fig. 4). External voltage multipliers 93 and 94 are used with the potential coilsof these meters. One terminal of the poten-- tial coil of meter 21 is connected through conductor 95, multiplier 93, conductorl 9B,c-ontacts 8 and 9 of switch S-I I, conductor 91, and conductor 16 to the center-taps of the filament transformer The other-terminal of the potential coil of meter 21 is connected to the current coil forward test as previously described.

The rectified plate power, exclusiveof that lost in the tube under test, is dissipated in the series load resistances. In testing 5.0 ampere tubes, the load resistors R-I, R-8, R-9 and R-I0 may be fixed 25 ohm resistors and are connected in parallel with each other and in series with variable resistor Rr6 which may be a 7.8 Ohm rheostat. In testing 2.5 ampere tubes the resistors R-I and R8 are disconnected from the load circuit by means of Load resistance switch SI 0; In testing 0.5 ampere tubes the fixed resistance R-II and variable R-I2 are added to the plate circuit. These resistors may have a value of 50 ohms each. i

The filament heating current is provided by a filament-grid transformer I00. The input voltage to the primary coil I02 of the transformer I00 is controlled by an 'auto transformer I03 which is connected across the line voltage as at I04 and is adjusted to supply the proper voltage which may be for example 117 v. The red indicator light 23 is connected across the circuit asat I05.

The input voltage is indicated by the Filament and pla voltmeter 29 which by means of switch S''I may be connected in either the plate or filament circuit; i i I The filament" grid transformer I00 has two secondary filament windings I06 and I0Iwhich for example may be of 2.5 volt rating each. Filament winding I06, which for example may have a current capacity'of 26 amperes, is connected to the filament terminals I08 of the mogul socket 35 through conductors [08a and to the filament terductors IIOa (see Fig. 4). Fig. 3 shows conductors I08a, I09a and I I0a connected directly to the filaments of the tubes under test. The filament windings I06 and I01 are center tapped as at III and I I2 to provide a returnfor the grid and plate circuits. A condenser H3 is connected from the center taps to the frame I2 of the tester in order to stabilize the grid. As a safety precaution to prevent possible electrical shock hazard if some circuit should be shorted tothe frame of the tester, the frame'l2 is groundedthrough the conductor I9 in thesupply cable (as described above). The grid voltage is obtained from a secondary winding II 4; which for example may be of 21 volt rating, on the filament grid transformer I00, and is rectifiedby a rectifier unit H5 to. supply D. C. voltage. "This rectifier unit H5 consists oi a vacuum tube rectifier I I6, a filtering condenser I", an adjustable resistor Bi-I8, and an adjustable resistor ='RI'I. The adjustable resistors R.IB and. R-I'l are so adjusted that when the input to the filament grid transformer I00 is maintained at rated value, potentials of from -15 volts to +6 volts relative to the center tap of the filament windings are available. To peraccess --ometer -rheostat R P-I is connected through :the grid resistors l -andfR- ii to the 'grid terminal as on the tohcdntrol panel is "(see Fig. 4) and through resistorsR- -l -"and R2"to the UX'soc'ket 1:3]. Fig. 3 for the purpose of illustration only,

shows a; direct connection from lit- 3 to "the grid of tube 48 op'posite the Mogul socket 35 and f'rom R2 to thegrid'of tube dil opposite the socket3'l. {The grid potential is determined-hem graduated dial 3=l'on the frontpanel adjacent to the grid control knob 30 (Fig. 2). This dial 30a. is graduated front +5to volts-in l-volt steps and at 1-5 volts with a designatlon marked Peak forward voltage. Thenormal grid. resistance-.R-l consists of a 10,000 ohm resistor which --is iniseri'es with a l megohmresistor 'R2 or R3 depending-uponwhich-testsocket is used. Re-

.sistorR-fl (asaforestated) is in the grid circuit *tothegridtermina-l above the Mogul and-Indus- .tri-al test sockets. Resistor R? is in the grid circuit to the-UX socket (seeFig. 4). These-grid resistors R3 and R2 are normally shunted as at I *and HM, respectively. The shunt I20 across -R--3 is 'removed for the grid current test by depressing push button switch S- -G. Likewise the -shunt 1.21 across R 2 is removed by depressing push button switch-S+5. The grid conduc- -tors-are-shielded-as at I122. -This shielding is grounded to the frame-lief the tester through conductor I23 and condenser I I-3.

-=For'test ingo.5 2.5"andampere tubes the voltmeter :29 has four'voltage rangesO-30, 0-60,

0450- and 0-450-which may beselectedbyinserting proper resistances R--I3, RI4, R--|5. Re-

sisto-rs :R--l 3 and R-'l4-a-re normallyin the plate --circuit'--giving' a voltage range of from 0- 150. The-0-'30 voltage range-may-be secured by de- 'pressingpush button switches S8 and 8-9 shunting both resistances 11-43 and R----l4. The 0-60 volt rangeis secured by depressing S-8 shunting resistance Rv-l3but leaving Rl4 in "the circuit. The 0- 4fi0'volt'range isselected automaticallyby'switch 8-4 I when the grid voltage control knob 30-is turned to peak forward voltage.

When the .grid' c0ntr01:kn0b-30 is turned to the Peak-forward voltage position the arc "drop "meter-potentials are disconnected and the additional transformer"M igconnected in'the plate circuit. This transformer HI-has a high second- "ary volta e 'rated 'for example-at 450 volts and I has an added load resistance :R -5 of for example 4500 ohms. "the voltmeter circuit'by -means of contacts 4 and "5 of'the switch S'--ll in addition to the resistanoes R.-l4 and 'R;"l'3 *normally in the circuit 7 The resistance R-l5 is placed in thus giving 'the'voltmeter'all-450 volt range.

As afore-"mentioned, the meters 21 and-28am calibrated 'to' r'eadarc' drop volts directly. The

"average arc-drop is the average ordinate of that portion of 1 the voltage cycle-indicated bythe shaded section on-"Fig. 1. An" accurate indication ofthis value; andhnewhichis unaifected by starting voltage "and" temperature, can be obtained' by' the "use-of a wattmeter and a D. C. -ammeter. The wattmeter is connected (as meters "21"a'nd'28 shown in Fig.3) so that the tube current passes throughits current coil-and the poten- --tial across the tube isapp'lied across its potential coil. The D. Cxammeter'is' connected in such a manner that it will measure the average value of the rectified current (as ammeter 26, Fig. 3)

-l3y examining the currentand voltage curves of "Fig. I it is seen that arc-drop occurs only when current is flowingthrough the tube. -Asa result the-average value of the: product of current and imitat mes enge V a ecfl e 34: v a e during ha tte th the wattrneter takes no r l W ur' etisne fifiw' e I t is PM? is divided by theaveragevalue of the current, the result will be the average value of the arc 3 drop "during that portion; of the cycle when the tube -is conducting. v For any particular D. C.

evriig t i r ntt ac e r m1 n liead .at 'i u a en ar fro fi l n eede W t Thus the dial 31 of arc drop or wattmeter 21 is calibrated toi indicate arc drop volts, for al). C.

ve a r n of. i er' e m l anewamperes -and the dial act are drop or watt- I meter '28; is cal ibratedto indicate arc drop volts is connected through; the socket '-to the base grid outlet of the-tube. 'When the Mogul socket 35 isused, both' 'the-plater'and grid connections must *be made. "In testing, for examplepSBI-ID tubes, 40

conductive bulkhead).

switch S- -'-l0- (Fig. 2) is set' to the positionmarked "to the Tzero plate -voltage position.

fora-DuC. average current of for example 0.5 r .l j Inoperation; in-testing tubes of. 0.5,-2.5 ;and 5.0

ampere rating, the supply cable i8 is connected to a-1 1-5 volt, 60 cycle A. Cjgsource and the ground conductor 19 is connected to a suitable ground (metal pipe, metalconduit, or a steel orother The load 'resistance i5BHD and GCF'tubeS'the switch S-IO is s et to the-position marked 2.5 -amp. When',tes ting full wave rectifier tubes, such'as F; the Plate transfer" switch 5-42 is set to No. 1.; Each 'plate'of full wave rectifier tubes is I tested-separately. Thi-s switch S-IZ is disregarded when testing ;grid"'icontrolled' rectifier tubes.

rThetube to be tested is now placed in the proper socket and grid and plate connections are made as required. Whenthe UK socket 31 is used'only theplate connection'ineed be made as the grid only the-plateconnector-is used. 7

Theplatevolta'ge control-knob 33 is-now turned The line switch sl'is closed" andthe red pilot light 23 comes "on, indicating thatipower is available for heating the filament. The filament voltage is now-adjusted by means 'of Filament voltage "control knob 3'2 until the proper filament voltlowedto heat tindshouldb'e red hot after about transformerBF to be connectedto the power'supage is indicatedon :the voltmeter 29. when the Press for filament voltage switch S| is closed. The filament'cfthe tube under test ;is now a1- a'minute. -At theend ofa pre'determined heating period, as for-example three minutes, the automatic timedelayrelay' 83 will close. causing the green-pilotlamp 22 tolight'and thepla'te-voltage ply.

The plate voltage is 'nowiincreased to 1 1,0,volts as indicated by voltmeter by turning the"P late voltage control" knob 33. At the same time the fPlatecurrent control--knob 24 is adjusted to *keep the plate, current from exceeding the operminutes :at the specified plate voltage and current to allow the tube to'attainits operating tempera.-

ture. To obtain consistent; test results, all test reading 'shouldbe taken as quickly as possible to prevent the tube fron cooling.

Test of jull-waverectifiers The arc-drop volt value is obtained by reading the arc-drop meter 21 directly. The proper scale on this meter must be read, however. The aredrop for type BI-ID and 6GB tubes, for example, is read on the scale of the meter 21 for 2.5 ampere tubes. i

The. plate voltage is now reduced by turning Platevoltage control knob 33 until the tube just ceases to fire. The A. 0. starting voltage is read. at this point on the Plate and filament voltmeter 29 using the scale changing push button switches S-8 and S-9, to obtain the appropriate scale on the voltmeter. i

The procedure is repeated for Are drop and A. 0. starting voltage with the second plate of the tube connected by means of switch S---l2.

} Test of grid-controlled rectifiers The Arc'drop volts value is read directly on the appropriate arc drop meter 21 or 28, For type ClA tubes the meter 28 for Arc drop 0.5 ampere tubes" is used. and for 05A and 06A tubes the meter 21 is used andthe reading is taken oil the scale for 5.0 ampere tubes.;

The Starting voltage is obtained by operating the tube at a grid bias of +3 volts D. C. (obtained by turning the Grid voltage control knob 30 until the point 30a indicates this value on the dial 3 l) with a load currentcorresponding to the tube rating, as for example 5.0 amperes, and gradually reducing the plate voltage from 110 volts A. C. by turning Plate voltage control knob 33 until the tube ceases to fire. The A. 0. starting voltage is read upon the voltmeter 29, again'selecting the proper scale with push button switches S8 and S---9.

The plate voltage is now returned by means of Plate voltage control knob 33 to its initial value of 110 volts. The load current remains that at which the tube is rated. The grid potential is now gradually changed to negative value by means of Grid voltage control knob 30 until the tube just ceases to fire. The Critical grid voltage is that value of the grid potential. as indicated by the point 301]. of the Grid voltage control knob upon the dial 3|.

The Grid control knob 30 is now immediately turned back to its +3 volt position. The "Grid current is determined by repeating the procedure for Critical grid voltage and determining the grid voltage with an additional one megohm resistor in the circuit (as aforementioned a 10,000 ohm resistance R-l is normally in the grid circuit) This is accomplished by depressing Grid current test switch S-5 placing 1 megohm resistance R-2 in the grid circuit when testing tubes of 0.5 ampere rating, such as type CIA, or by depressing Grid current test" switch S--6 placing 1 megohm resistance R-3 in the grid circuit when testing tubes of 5 ampere rating, such as type C5A or 06A, and carrying out the test procedure with the proper button depressed. The difference in the reading of the dial 3| with the one megohm resistance in the circuit (i. e., with the appropriate switch S5 or S-B depressed) and with the one me ohm resistance out of the circuit is equal to Grid current in microamperes. Since the actual potential on the grid is the same when the tube ceases to fire in both cases this may be proven as follows: I

Lettin Ea =Actual potential on grid at cut oil? In =Grid current, R1 in circuit I =Grid current, Rl and R2 in circuit Eg1=Indicated grid potential with R1 in circuit R1 =10,000 ohms E 2=Indicated grid potential with Rl and R2 in Since R1 is approximately one percent of R2, it can be assumed that R1 is zero, hence:

Eg1-Eg2=I microamperes Hence, the grid current in. microamperes is equal to the difference in grid indications.

The final test is the maximum or R. M. S. forward voltage. The plate voltageiis reduced to a low value by turning Plate voltage control knob 33. The Gridvoltage control knob 30 is turned to the Peak forward test position and held in place. This provides a negative grid bias of -15 volts and operates switch S-I| to provide plate voltage in the 0450 volt range. The plate voltage is now increased untilthe tube fires between the cathode and plate. The R. M. S. forward voltage is read on the 450 volt scale of the voltmeter 29. f

In shutting down the tester the Plate voltage control knob is returned tothe zero position, the line switch 8-4 is turned off, theplateand grid clips are removed, and the tube under test is removed fromits socket. 1 i

A summary of tube test conditions using the electronic tube tester. of this invention for tube types ClA, C5A, 5BHD, and 601? is as follows:

. GSA 5BHD Tube Type CIA and and 06A 60F Filament Voltage 2. 5 2. 5 2. 5 Filament Heating time, minutes. 3 3 3 Grid resistance, ohms 10, 000 10, 000 Pro-test operation time, minutes 3 3 3 Pro-test Operation Conditions:

Plate Voltage. 110 110 Plate Current (Amp D C 0.5 5.0 2.5 Grid Voltage +3 +3 Arc Drop Test:

Plate Voltage 110 110 110 Plate Current 0. 5 5. 0 2. 5 Grid Voltage +3 +3 Starting Voltage Test:

Plate Current (start) 0. 5 5. 0 2. 5 Grid Voltage +3 +3 Grid Current Test:

Plate Voltage 110 110 Plate Current 0. 6 5 Grid Rcsistance Ea Critical Grid Voltage Te Plate Voltage Plate Current (start) 0. 5 5. 0 Forward Voltage Test (R. M. 8.):

Grid Voltage l5 l5 It is to be understood that various modifications and changes may be made in this invention Without departing from the spirit and scope thereof as set forth in the appended claims.

The invention described herein maybe manufactured and used by or for the Government or 11 the United States of America for governmental purposes Without the payment of any"royalties thereon or therefor.

What is claimed is:

1. A voltmeter for measurin the voltage drop across an electron-discharge tube during periods of conduction, said voltmeter comprising a wattmeter connected across the plate and cathode circuit of said tube, and an ammeter serially, connected in the plate circuit or said tube, said ammeter connection being such as to make said wattmeter responsive to and indicative of average arc-drop voltage in the tube tested.

2. In an eIectr nictube'tester having means for testing electron discharge tubes of diverse types, '-each;said ,tube having respective platecathode circuits,'the combination comprising a multiple-range arc-drop indicating device; means conjointly connecting" said plurality of platecathode circuits to said multiple range arc-drop indicating device, and means for automatically selecting one ofthe ranges of said multiple range indicating device correspondingto a predetermined operatin'g characteristic of one of said electron discharge tubes.

3. In an electronic tube tester having a plate circuit and a cathode circuit, each adapted to be connected to a power source, and having a plurality'of sockets for receiving tubes to be tested, the improvement-comprising ammeter means connected' to measure the plate current passed by a tube during test, a plurality of power measuring devices connectedin the plate and cathode circuits to measure the power expended in said tube, and meanis associated with atleast one of said socketsfor-automatically selecting one of said power-measuring devices upon the insertion of a tube in said one socket, whereby a predetermined one of said power-measuring devices may be selected for use with the particular tube insertedyj" 4; In a tester for electron-discharge tube having a plate cathode ,circuitjconnectedto a source of"po wer for" establishingan'electric discharge throughsaidftube, thefcombination of wattmeter means having a current con, a potential coil and dial face, the current coil of said wattmeter means being connected in seriesiin the plate circult-to receive a rectified current, the potential coil of said "wattmeter means "being connected 12 across the plate circuitso asto receive plate-tocathode potential; and h dfal fa organ-wat meter means being "calibrated to'mdica'te directly are drop volts, for aserig f; applied values of average current} 'f j f 5. Electrical test apparatus for an electron-discharge tube having 11a" "cathode and an anode adapted to be interconnected "to define plate circuit, said apparatus'com'prising afirstelctri cal-quantity measuringdevice including a current-responsive member in series with said; plate circuit and avoltage iespoiisive'member in s hiint withsaid plate circuit,"said'currnt afidvoltage? responsive nfemb'ers being Telativelymovable normallyto provideari indication or 'the power'ex pended during 'interva1s'or conduction of current in said plate circuit: a second electrical-quantity measuring devicd'havlng 'a currr'it r'spon'sive member'in series with said-plate circuit for indieating the "current new 'in'said plate circuit, means for adjusting the magnitude' or currerit'in said plate circuitto a predeterminedvalue, and indicia cooperab'le with said "first electric measuring device for indicating the quotient of'the magnitude of said expnded? power and the predetermined current valujefin said platei'cirouitt "6. 'A 'method of testing: anjelectric discharge tube for arc drop. voltage; s'aidimethod comprising subjecting said tube to-conditions suchithat a pulsating unidirectional current passes through said tube, applying a varying voltage to said tube while said icui'rent passes, and deriving. an indi-i cation correspondingtoltheiquotien'tof.;the5aver+ age power expended. insaidLtube a'ndthe. current passing th'erethroughn i" t A ALBER'ILS.',ORAVE.TZ.

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